1. Field of the Invention
This invention relates to a method for manufacturing a cable used as a stay in a cable-stayed bridge.
2. Description of the Related Art
In general, a Parallel Wire Strand cable (PWS) is used as a stay in a cable-stayed bridge. The PWS consists of a bundle of plural wires arranged parallel with one another, and has a high breaking-load strength and a high elastic coefficient. Thus, the PWS has superior properties for use as a stay in a cable-stayed bridge.
Such a PWS is carried from a manufacturing plant to a bridge-construction site, wound on a reel. It is difficult to wind the PWS onto a reel neatly and a substantial amount of time and labor are required to do so, since the bundled parallel wires of the PWS can easily deform.
To overcome the disadvantages, the development of a cable which has a rope structure in which the wires are stranded has been considered. In this case, however, each of the wires may be deformed plastically, since it is stranded about its axis, causing the so-called "reduction in breaking strength due to stranding" (i.e. reduction in strength resulting from multiplying a linear wire strength by a spining factor). This breaking strength reduction decreases the breaking-load strength and elastic coefficient of the cable, making it difficult to maintain the best properties of a cable to be used as a stay in a cable-stayed bridge.
In view of the above-described circumstances, a method for manufacturing a cable suitable for a cable-stayed bridge has been developed (see Jpn. Pat. Appln. KOKAI Publication No. 3-60954). The cable obtained by the use of this method has substantially the same breaking-load strength and elastic coefficient as a PWS, and can be wound on a reel without causing great deformation of the cross section due to stranding.
Recently, large cable-stayed bridges, such as channel bridges, have been constructed; and accordingly a cable of as long as 300-500 m has been required. In producing such a long cable, closing dies and panel plates must be located in a linear pass-line with the approximate same length as that of the cable. This means that a facility as long as the cable must be built on the manufacturing plant site. In reality, however, it is difficult to construct such a long facility on the site.